This example deals with application of SBRA (Simulation Based Reliability Assessment) method for safety assessment of a welded steel beam with a sudden profile variation. Close attention is paid especially to the determination of the position where the profile changes.

The beam is simply supported. Span is L = 4 m, material grade is steel S235. The beam is exposed to two uniformly distributed loads. The design values are: dead load g = 10 kN/m, long lasting live load q = 8 kN/m. Assess I-profiles of this steel welded beam (see Fig. 2) regarding the bending moment. Determine the position where the profile is to be changed with respect to the material savings. Lateral-torsion buckling of the beam is prevented. Do not assess the serviceability limit state. The design probability of failure is Pf,lim <= 0.00007.

The variable value of the load is equal to the product of its maximum value and the coefficient expressing its variation by the assumptive distribution, then g = 10 kN/m ∙ gvar, q = 8 kN/m ∙ qvar. Individual distributions follow in the chart (Fig.3).

The variable value of the steel yield stress is equal to the coefficient expressing its variation by the assumptive distribution, then f = fvar. The variable values of the profile moduli are equal to the products of their nominal values and the coefficients expressing their variation by the assumptive distributions, then W1 = W1,nom ∙ Wvar, W2 = W2,nom ∙ Wvar. Individual distributions follow in the chart (Fig.5).

This study outlines the opportunity of using SBRA method for the global reliability assessment. The used example is very simple; however, it is possible to asses more complicated statically determined structures.